STREPTOCOCCUS PYOGENES. STREPTOCOCCUS PYOGENES Streptococci are potentially pathogenic Gram-positive micro-organisms growing in pairs or chains. They occur as normal hosts in man. Streptococci are divided into four groups, A, B, C and D, according to the antigenic properties of the polysaccharides on their surface. They are normally found in the human alimentary tract but can cause severe infection, including scarlet fever and erysipelas. SEM of Streptococcus A or Streptococcus pyogenes (3000